Most people (about 80 percent) do not show symptoms of West Nile infection, with about 20 percent exhibiting mild symptoms such as rash, fever and headache. One in 150 people develop of severe form of the illness that presents with neurological symptoms such as tremors, vision loss and numbness, according to the CDC.

West Nile is not spread through “casual touch” but rather through mosquitoes and medical procedures such as transfusions when blood is exchanged (this is rare as blood is screened for the virus), according to the CDC.

West Nile also affects horses, and has an up to 40 percent fatality rate in the animals, whether they die from the resulting illness or must be euthanized.